Generally automatic roll-shifting roll stands are used for high speed rotational printing machines. These automatically operating roll stands are designed in such a way, that when the unwinding roll almost is finished, the new roll automatically or through manually actuated signals will start rotating, driven either by central means or by means of driving belts, which are pressed against the periphery of the roll. Well-tried and functioning systems are used to carry out the joining, the so called flying pasting.
For the required synchronization between the speed of the unwinding web and the circumferential speed of the new roll conventional electronic comparative systems are used comprising pulse transducers, current converters and similar components. These systems are comparatively complicated and are not capable of ensuring a complete synchronization. Also, often various control systems are used for the braking and the acceleration, which during various phases are required in connection with the shifting process, which provides an additional complicating factor.
Also, sometimes it is necessary to load the roll stand laterally and not, as is the conventional way to do it, between the printing units and then forward towards that roll stand which belongs to the printing machine. The reason for this is a desire to build the entire plant more compact, which however makes it more difficult to simultaneously also obtain an uncomplicated yet very efficient roll shifting.